A. Field of the Invention
The device of the present invention generally relates to molded case circuit breakers and, more particularly, to electrical contacts used in such circuit breakers.
B. Description of the Prior Art
Circuit breakers and, more particularly molded case circuit breakers are old and well known in the prior art. Examples of such devices are disclosed in U.S. Pat. Nos. 3,525,959; 3,614,685; 3,815,059; 3,863,042; 4,077,025; and 4,166,205. In general, prior art molded case circuit breakers have been provided with movable contact arrangements and operating mechanisms designed to provide protection for an electrical circuit or system against electrical faults, specifically, electrical overload conditions, low level short circuit or fault current conditions, and, in some cases, high level short circuit or fault current conditions. Prior art devices have utilized a trip mechanism for controlling the movement of an over-center toggle mechanism to separate a pair of electrical contacts upon an overload condition or upon a short circuit or fault current condition. Such trip mechanisms have included a bimetal movable in response to an overload condition to rotate a trip bar, resulting in the movement of the over-center toggle mechanism to open a pair of electrical circuit breaker contacts. Such prior art devices have also utilized an armature movable in response to the flow of short circuit or fault current to similarly rotate the trip bar to cause the pair of contacts to separate. At least some prior art devices use blow-apart contacts to rapidly interrupt the flow of high level short circuit or fault currents. In such desvices, the lower electrical contact of the blow-apart contacts may be stationary; or it may be movable. Stationary lower electrical contacts have often required the use of shims or trial and error procedures to precisely adjust the position of the electrical contact above the base of the circuit breaker. In addition, stationary lower electrical contacts used in the prior art are not conducive to adjustments in contact pressure and often require the changing of the operating springs used in the circuit breaker in order to obtain higher contact pressure for higher current ratings.
While many prior art devices have provided adequate protection against fault conditions in an electrical circuit, a need exists for dimensionally small molded case circuit breakers capable of fast, effective and reliable operation and, more specifically, for a compact, easily adjustable stationary lower electrical contact.